Regional oximetry, also referred to as tissue oximetry and cerebral oximetry, enables the continuous assessment of the oxygenation of tissue. The measurement is taken by placing one or more sensors on a patient, frequently on the patient's left and right forehead. Regional oximetry estimates regional tissue oxygenation by transcutaneous measurement of areas that are vulnerable to changes in oxygen supply and demand. Regional oximetry exploits the ability of light to penetrate tissue and determine hemoglobin oxygenation according to the amount of light absorbed by hemoglobin.
Regional oximetry differs from pulse oximetry in that tissue sampling represents primarily (70-75%) venous, and less (20-25%) arterial blood. The technique uses two photo-detectors with each light source, thereby allowing selective sampling of tissue beyond a specified depth beneath the skin. Near-field photo-detection is subtracted from far-field photo-detection to provide selective tissue oxygenation measurement beyond a pre-defined depth. Moreover, regional oximetry monitoring does not depend upon pulsatile flow.
Regional oximetry is a useful patient monitoring technique to alert clinicians to dangerous clinical conditions. Changes in regional oximetry have been shown to occur in the absence of changes in arterial saturation or systemic hemodynamic parameters.